Small cell osteosarcoma is rare, representing 1-4% of all osteosarcomas. We experienced a case of small cell osteosarcoma in an 8-year-old girl on her calcaneus. Histologically, the tumor consists of small round cells that resemble those of Ewing's sarcoma, and variable foci of lacy osteoid formation between tumor cells. The rare location, histologic characteristics and differential diagnostic points are discussed.